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Axinelloside A was isolated from the lipophilic extract of the Japanease marine sponge Axinella infundibula collected off Shikinejima Island as a strong human telomerase inhibitor (IC_<50> 2.0μg/mL). The ^1H and ^<13>C NMR spectra suggested axinelloside A to be a highly sulfated lipopolysaccharide. The sugar composition was determined by GC and GC/MS analyses of the alditol acetate derivatives of the acid hydrolysates, whereas fatty acids were identified by FABMS and NMR data of both alkaline and acid hydrolysates. Together with these results, interpretation of 2D NMR data of axinelloside A could determine not only the sequence of sugars but also the position of fatty acids (Figure 3). The deuterium isotope shift experiment indicated that the 19 oxygen-linked carbons were sulfated. MS analyses confirmed the complete structure of axinelloside A including the glycosyl sequence. Axinelloside A consists of twelve sugars, e.g., a scyllo-inositol, a D-arabinose, five D-galactoses, and five L-fucoses, together with a (R)-3-hydroxyoctadecanoic acid, three (E)-2-hexadecenoic acids, and 19 sulfates (Figure 7). The molecular formula of axinelloside is C_<137>H_<219>O_<117>S_<19>Na_<19> as the 19 sodium salt.